The exhaust gas discharged from internal combustion engines, e.g., automobile engines, contains harmful components such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx). Exhaust gas purification catalysts are widely used in order to efficiently remove these exhaust gas components. Exhaust gas purification catalysts are typically provided with a catalyst layer that contains a precious metal that functions as a catalyst (also simply referred to as a “catalyst metal” herebelow) and with a support that supports this catalyst metal.
A problem with these exhaust gas purification catalysts is that the catalyst metal deteriorates, for example, under long-term exposure to high-temperature exhaust gas, and the purification performance then declines. A primary cause of this is the sintering (particle growth due to sintering) of the catalyst metal under high-temperature conditions (for example, 800° C. to 1000° C.). That is, when sintering of the catalyst metal advances, the specific surface area declines and fewer catalytically active sites are present. The exhaust gas purification performance may decline as a result. Various investigations have thus already been carried out in order to inhibit this phenomenon. For example, Patent Literature 1 teaches that particle growth by the catalyst metal can be inhibited by using, as the support, alumina that has an average interlayer distance controlled to 0.01 to 0.1 μm.